The invention relates to heat treatable coated glass panes with a solar control coating. The invention also relates to multiple glazings incorporating said panes.
Heat treated glass panes which are toughened to impart safety properties and/or are bent are required for a large number of areas of application, for example for architectural or motor vehicle glazings. It is known that for thermally toughening and/or bending glass panes it is necessary to process the glass panes by a heat treatment at temperatures near or above the softening point of the glass used and then either to toughen them by rapid cooling or to bend them with the aid of bending means. The relevant temperature range for standard float glass of the soda lime silica type is typically about 580-690° C., the glass panes being kept in this temperature range for several minutes before initiating the actual toughening and/or bending process.
“Heat treatment”, “heat treated” and “heat treatable” in the following description and in the claims refer to thermal bending and/or toughening processes such as mentioned before and to other thermal processes during which a coated glass pane reaches temperatures in the range of about 580-690° C. for a period of several minutes, e.g., for up to about 10 minutes. A coated glass pane is deemed to be heat treatable if it survives a heat treatment without significant damage, typical damages caused by heat treatments being high haze values, pinholes or spots.
It is desirable to be able to manufacture a range of coated glass panes with a variety of light and/or heat transmission values in order to meet particular needs. One approach to address this objective is to use a common multilayer stack or platform for each of the different product types (e.g. low-e and solar control, and both heat treatable and non-heat treatable products) and then tune the optical properties of the stack by adding different thicknesses of at least one absorbing layer into each of the stacks.
In the context of the present invention, where a layer is said to be an “absorbing layer” this means that the layer has measurable absorption within the solar energy spectrum, including but not limited to the visible part of the spectrum. Such an absorbing layer may therefore serve the general purpose of controlling (reducing) the solar energy transmission through coated glass panes.
Certain absorbing layers are known in the prior art. For instance, EP 0718250 A2 describes a coating stack with a protective metallic layer (e.g. Nb, Ta, Ti, Cr, Ni, NbTa, TaCr, or NiCr) located directly above a functional metallic layer such as silver. The thickness of the protective metallic layer may be modified to adjust the light transmission.
WO 2008/075107 A1 describes the use of tungsten nitride barrier layers as absorbing layers, preferably both directly above and below a silver-based functional layer. To achieve a sufficient barrier and solar control function the barrier layers comprising tungsten nitride WNx (x<1) should have a thickness of at least about 2 nm. The fact that the barrier layer must have a minimum thickness (in order that the barrier layer adequately protects the silver-based layer against the reactive plasma during reactive coating of the subsequent dielectric layers) means that the thickness of the tungsten nitride layer is restricted, such that there is not complete freedom with regard to the optical properties that can be attained. Furthermore, the adhesion of barrier layers based on tungsten nitride to a silver-based layer was found to be lower than the adhesion of other barrier layers. Low adhesion between individual layers of a coating stack may lead to delamination of the coating stack, e.g., during heat treatments.
WO 2009/067263 A1 describes coatings with at least two silver layers which may be protected with absorbing barrier layers. The absorbing barrier layers may be selected from a wide range of materials, although NiCr is preferred. NiCr-based absorbing layers tend to oxidise during heat treatments and thereby change their optical properties significantly.
WO 2009/001143 A1 discloses coated glass panes wherein an absorbing layer is embedded in an Al (oxi)nitride layer being part of an anti-reflection layer of a low-e and/or solar control coating stack. The absorbing layer may comprise a metal or a metal nitride, preferably NiCr, tungsten or their nitrides. Such arrangement increases the complexity of the stack.